The present invention relates generally to test tube sealing caps used in centrifuge rotors and, more particularly, is related to sealing arrangements used for not only sealing test tubes, but also sealing the rotor tube cavity in which the test tube resides.
Analytical and comparative centrifuges are commonly provided with a rotor having a series of cavities which are arranged in a generally circular orientation for receipt of test tubes carrying a sample to be centrifuged. In many prior art rotor cavity arrangements the axis of each cavity is annularly oriented with respect to the vertical rotational axis of the rotor, so that the bottom of the test tube is further away from the rotor axis than the top. An example of such an annularly oriented rotor cavity rotor is shown in FIG. 5 of U.S. Pat. No. 2,878,992 issued to Pickels et al. on Mar. 24, 1959 and assigned to the assignee of the present invention.
During centrifugation the sample, which is initially in the lower end of the test tube, attains a somewhat vertical orientation which is essentially parallel to the rotor axis. Because of the orientation of the test tube in the rotor a portion of the sample reaches the upper end of the test tube and exerts a significant amount of loading on the capping arrangement at the upper end of the test tube. Consequently, because of the high G forces experienced by the test tube capping arrangement, it is extremely important to design a sealing arrangement on the test tube to retain the sample fluid within the test tube and prevent possible escape of the fluid from the rotor which may cause a serious imbalance in the rotor, resulting in serious damage not only to the rotor but to the drive system.
An exemplary solution to the particular problem of sealing the upper end of the test tube is shown in U.S. Pat. No. 3,938,735 issued to Wright et al. on Feb. 17, 1976 and assigned to the assignee of the present invention. This patent discloses the use of a test tube cap assembly which deforms inwardly the flexible test tube at its upper end to squeeze the upper end of the tube between respective slanting surfaces of the stem member and the crown member to effect a fluid tight seal. Another approach to sealing the upper end of the test tube is shown in U.S. Pat. No. 3,447,712 issued to M. Galasso, et al. on June 3, 1969 and assigned to the assignee of the present invention. This patent discloses the use of a crown member and a stem member in conjunction with an O-ring to seal the top of the test tube.
Recently, however, rotors have been designed which incorporate a series of vertical tube cavities oriented in a circular fashion around the rotational axis of the rotor. In such a configuration the sealing of the test tube sample within the tube itself as well as within the rotor becomes extremely critical, since even a greater amount of the fluid sample will be exerting higher centrifugally induced forces on the upper end of the test tube during centrifugation than in fixed angle tube rotors. Typically, the type of test tube utilized is a thin flexible material which in some instances may have a weak point which under the high G loading exerted by the fluid could result in possible leakage, allowing fluid to escape out of the rotor and resulting in possible damage to the rotor.